For Google+, you probably want
https://www.googleapis.com/plus/v1/people/me/people/visible
(Providing your auth token, and possibly limiting it to particular fields if you want.) Keep in mind there are some limitations of what you'll actually get back - only public information is available, so if the user has limited the visibility of the circles they share, you won't necessarily see everyone.
See https://developers.google.com/+/api/latest/people/list for full details.